Evacuating electric discharge device



June 4, 1929. H. c. RENTSCHLER 1,716,149

EVACUA'I'ING ELECTRIC DISCHARGE DEVICE Filed Feb. 1, 1927 WWW.

ATTORNEY if atented June 4,- 1929.

PATENT OFFICE.

UNITED S'I'ATES HARVEY CLAYTON RENTSCHLER, OF EAST ORANGE, NEW JERSEY,ASSIGNOR TO WESTINGHOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

EVACUATING ELECTRIC DISCHARGE DEVICE.

Application filed February 1, 1927. Serial No. 165,092.

This invention relates to the removal of gases from solids and to thecreation of high vacua in discharge devices. More particularly theinvention relates to the removal of gas from conductive bodies, such aselectrodes, lead wires, supports and other metal bodies in electricaldischarge devices and to the method of expediting the exhaust thereof.

In the manufacture of electrical discharge devices it is the usualpractice to sub ect the mount before sealing-in to the envelope, to aheat treatment in vacuum or in a reducing gas, such as hydrogen, toliberate the gases therefrom as completely as posslble and after theelectrodes have been incorporated into the envelope, to heat theelectrodes bv bombardment or high frequency induction currents to driveoff the gases therefrom. In spite of this careful treatment, however,serious difficulty is BXPGII- enced, due to further release of gasduring operation from such of the metal parts of the device which it wasimpossible to heat treat in this manner, thus causing an impairment ofthe vacuum and changing the characteristics of the device, oftenrendering the same inoperative. This is particularly troublesome in highvacuum devices employing high plate voltages. The same difficulty isobserved, however, in the manufacture of gaseous discharge devices, suchas discharge lamps, rectifier-s, etc., employ ng a rare gas filling asargon, neon or helium. In such devices the gas becomes contan'iinatedwith common gases and impurities given off by the metal parts of thedevice during operation, causing the starting and operatingcharacteristics thereof to be changed often to such a. degree, as torender the device in capable of operation or operable only at materiallyhigher volta es.

It is one of the ob ects of the present 1nvention, therefore, to providea new method of effectively removing the gases from the electrodes, leadwires, supports and other metal and glass parts of an electric dischargedevice and to produce a device, the characteristics of which will not bealtered by gas evolution during operation thereof. A further object isto provide a method of removing gases from such metal parts which areclosely adjacent the glass without subjecting the same to heat treatmentor creating cracks or strains in the adjacent glass.

Another object is to provide a discharge device which may be operatedthroughout a long commercial life without appreciable change in thevacuous condition thereof.

A still further object is to provide an improved method of exhausting adischarge device which is simple and effective and which materiallyreduces the time required for obtaining a high vacuum therein.

Other objects and advantages will hereinafter appear.

It has been found that the metal parts of the device, after the bakingout thereof and prior to mounting in the discharge device, become coatedon the surface with an appreciable amount of gas and impurities and thatsuch gas and impurities adhere very tenaciously so that they are notremoved by the pumping operation. In the case of the electrodes, the gasand other impurities may be driven off by the bombardment or highfrequency treatment thereof but the portions of the device lyingadjacent the glass are difiicult to treat, due to the fact that heatradiated from the electrodes to the lead wires and supports isinsufficient to effect a removal of gas therefrom and moreover, even ifit were possible to heat the metal adjacent the glass sufficiently todrive the gases therefrom, the heat would cause the glass to crack,rendering the device defective. It will be understood therefore, thatwith the methods in vogue for removing the gases from the electrodes ofdischarge devices that the leading-in wires and other metal parts, inthe vicinity of the glass, are not sufficiently treated and when theapparatus is later operated, gases or vapors are given off which impairthe operation of the apparatus. In accordance with the present inventiona discharge device is exhausted by the usual pumping methods and duringsuch exhaust the bulb is baked in the usual manner at a sufiicientlyhigh temperature to drive the gases and water vapors from the surface ofthe glass and in the case of devices employing incandescent cathodes,the cathode is heated by a passage of current to drive off the gases onthe surface or occluded therein. After the removal of the majorportion'of the gas in this manner a high potential, high frequencyelectrical discharge is passed between the electrodes to create a strongelectrostatic field in the device. This high voltage discharge causes avigorous sparking directly between the metal parts and particu larlythose parts adjacent the glass, since as is well understood, such adischarge tends to take the longest path possible through the residualgas. By virtue of the high vacuum which was produced prior to the highfrequency discharge, there is very little heat produced by the dischargeand the removal of the gas from the surface of the metal is effectedwithout danger of causing the glass to become cracked or having strainsset up therein.

The action of the discharge appears to be to create an electrostaticfield which pulls the occluded or closely adherent gases or vapors andother impurities from the leading-in wires and from the electrodes andpermits them to be removed by the pump which is operated continuouslyduring this operation. The high frequency, high voltage operation shouldbe continued until further ionization and sparking within the bulbceases. The voltage employed when using high frequency current may bevery high Without danger to the envelope or other parts of the deviceand preferably should be several times the voltage to which the deviceis to be later subjected in operation, thus, for instance, if the devicebeing exhausted is designed to operate at 10,000 volts it is preferableto employ a high frequency, high voltage discharge having a potential of25,000 to 50,000 volts or higher. If the operating voltage is around100,000 volts,

' such as employed in X-ray tubes and similar devices, the metal partsshould be treated out with a high frequency discharge of 150,- 000 to200,000 volts. The frequency of the current should be sufiiciently highto render the operation safe and may range from 20,000 to 500,000 ormore cycles per second.

After the denuding of the metal parts in this manner the electrodes areheated to a high temperature, either by electron bombardment or by highfrequency induction currents to drive out the gases contained in theinterior thereof and at the same time, these gases are cleaned up by ametallic clean-up agent having a high aflinity for such gases ashydrogen. Preferably, aluminum is employed as the clean-up agent sincealuminum may be applied directly to the electrode and by virtue of itshigh vaporization temperature, it is possible to practically completelydegasify the electrode before the aluminum is vaporized. Uponvaporization of the aluminum the gases liberated by the electrodesduring heating are cleaned-up and the aluminum deposited on the walls ofthe envelope where it serves throughout the life of the device tomaintain the vacuum therein in a first class condition. By cleaning upthe gases liberated almost instantaneously in this manner, the danger ofthe gases redepositing on other parts of the device is very much reducedand the time of exhaust considerably decreased.

However'gdn order to insure the complete cleaning of the metal parts ofgases I prefor to again subject these parts to another high frequency,high voltage discharge prior to scaling off of the device. It is to beunderstood, of course, that throughout the entire operation ofexhausting and removing the gases from the interior parts, that thepumps are maintained continuously in operation and the gases are removedfrom the device as they are detached from the metal to which they sotenaciously adhere.

In order that the invention may be more fully understood reference maybe had to the accompanying drawing in which the single figureillustrates a high voltage electron discharge device and circuitarrangements for subjecting the same to my improved exhaust treatment.

The discharge device illustrated consists of a glass envelope 1containing an anode or plate electrode 2 and a filamentary cathode 3.The anode consists of a cylindrical plate supported from a reentrantstem 4 of the device by a pair of metal supports 5 secured to a metalcollar 6 clamped about the reentrant portion 4 in any desired manner.Current is conducted to the anode 2 by a. leading-in wire 7 joined tothe supports 5 by a cross bar 8. The leading-in conductor 7 is inelectrical connection with the terminal 9.

The cathode 3 is in the form of a looped or hair pin shaped filamenthaving its ends supported by and secured to the leading-in conductors 10and 11 sealed through the press 12 at the opposite end from thereentrant portion 4. The bight of the filament is supported by a metalrod 13 also sealed in the press. A. quantity of aluminum 14 is securedto the plate in any suitable manner, such as welding, or may be retainedthereon by striking out a strap from the plate material and insertingthe aluminum strip thereunder. The envelope 1 is connected to an exhaustsystem in any suitable manner as by the exhaust tube 15. l a

Any desired apparatus may be employed for supplying the high voltage,high frequency current to the device and as shown, the secondary 16 of ahigh frequency or Tesla coil 17 is connected by current conductors 18and 19 to the terminals of the device. A switch 20 is provided forcontrolling the high frequency, high voltage discharge.

A source of current, such as battery 21 is provided for heating thecathode to an electron-emitting temperature and a suitable source ofdirect current, such as a generator 22, having a voltage in excess ofthe voltage Ill well known in the exhaustin for which the device isdesigned to operate is joined to the respective terminals of the devicethrough a switch 23. A SW1t0h 24 is also provided for controlling thefilament heating current.

In carrying out the exhaust treatment b means of the apparatusillustrated, the bul is first connected to the exhaust tube 15 and thepumps operated until a high vacuum is obtained. The switch 24 is thenclosed and the filament 3 heated to cause the ases contained therein tobe liberated, the pum meantime being operated to I remove suc gases fromthe envelope. During th1s treatment and the succeeding treatments, thebulb is heated from the exterior, in the manner of such devices, todrive ofi the gases an vapors therefrom and to prevent the same fromrecondensing or collecting on the surface thereof. After the preliminaryvacuum has been obtained in this manner the high frequency, high voltagedischarge is passed through the device by closing the switch 20, thusenergizing the Tesla coil 17. This discharge 1s continued as long assigns of gases are shown but it is to be understood that, due to thedegree of vacuum in the device, that'the electrodes and metal .parts,particularly those parts adjacent the glass, remain comparatively cool.At the completion of this treatment the switch 20 is opened and theswitch 23 is closed to pass a direct current .or low frequency dischargebetween the electrodes 2 and 3. This discharge should be of sufiicientlyhigh potential to heat up theelectrode 2 to a high. incandescence, byelectron bombardment, thus driving oif the gases therefrom andpermitting them to be removed from the device by the pumps. A voltagesomewhat in excess of the normal operating voltage of the device shouldbe employed. After the degasificatlon of the anode, the discharge isincreased to further raise the temperature of the plate suflicientlyhigh to effect a vaporization of the aluminum 14 on the plate. Thealuminum, upon vaporization, immediately cleans up all gases given offby the plate or residual gas in the envelope, thereby greatlyjfacilitating the exhaust process. It then'deposits upon the wall of theenvelope where it serves throughout the life of the device to clean-upany gas which may be liberated as from the plate, during operation.Aluminum is particularly effective in cleaning up hydrogen and sincehydrogen is a troublesome gas in devices of this nature and is verydiflicult to remove by the usual clean-up material, such as magnesium, Iam enabled to obtain and maintain better vacua with devices employingvery high voltages than has heretofore been possible. After the flashingof the aluminum, the switch 23 is opened to discontinue the bombardmentas is also the switch 24 and preferably the high frequency, high voltagetreatment is a ain. given to the device for a short time to msure theremoval of any gas which may have de osited on the metal adjacent theglass durm the degasification of the plate electrode. uring this entirecriod, the pumps are maintained in operation and the'gases are removedfrom the device as fast as they are detached. The tubulature 15 may thenbe sealed oil".

It will be noted that a process has been devised which is effectivefirst for ridding both the glass and metal parts of adherent gases whichmight be liberated during the operation of the device and that incooperation therewith a substance is provided within the envelope forassisting in maintaining the high vacuum so originally created. Byvirtue of the cooperation of these two features 1 am enabled to producedischarge devices which may be operated at several hundred thousandvolts without signs of ionization and which have a long life withoutimpairment of the vacuous condition therein.

It is, of course, obvious that many changes may be made in the exactdetails of the process from that described and I do not desire to belimited to the precise order of steps given herein except as defined inthe appended claims.

What is claimed is:

1. The method of removing adherent gases and vapors from the metal partsof a discharge device, closely adjacent the glass, consisting increating a high voltage electrostatic field between the metal parts, ina vacuum to detach the gases therefrom and removing the gases from thedevice as they are detached.

2. The method of creating and maintaining high vacua in dischargedevices comprising detaching the gases from the metal parts of thedevice ad acent the glass by a high voltage, high frequency dischargetherebetween, removing the gases so detached from the device andvaporizing a metallic clean-up agent in the device which serves duringoperation of the device to assist in maintaining the vacuuous condition.

3. The method of creatin and maintaining a high vacuum in an el ectricdischarge device, comprising establishing a hi h voltage electrostaticfield in the device between the parts to be degasified to detach gasestherefrom, removing the gases from the device, and vaporizing a metallicclean-up agent therein.

4. The method of creating and maintaining a high vacuum in an electricdischarge device comprising creating an initial vacuum passing a highvoltage, hi h frequency discharge throu h the device etween the parts tobe degasi ed to detach the surface gases therefrom, heatin theelectrodes to a high temperature to rive the occluded gases highfrequency discharge therethrough to detach the surface gases from themetal parts adjacent the glass, passing a high voltage, direct currentor low frequency discharge through the device to drive the occluded asfrom the electrode, said discharges oth having a potential in excess ofthe operating potential of the device, and vaporizing a uantity ofaluminum in the device to faci itate the exhaust and maintain thevacuous condition during the operation of the device.

In testimony whereof, I have hereunto subscribed my name this 31st dayof J anuary 1927.

HARVEY CLAYTON RENTSCHLER.

